This work seeks to understand the internal mechanisms responsible for the movements of flagella and cilia. These include the dynein- microtubule interaction responsible for active sliding, the oscillatory mechanism, and control mechanisms that determine a particular type of bending pattern and its parameters. Because of the importance of cilia and flagella in normal respiratory and reproductive functions (as evidenced by the pathology of "immotile cilia syndromes"), an understanding of the functioning of these organelles is important in its own right. In addition, simple flagella provide a particularly accessible and highly organized system that appears to be the best source of detailed information about microtubule-mediated motility, which can be extended to increase our understanding of other systems such as mitosis, axonal transport, and the crossbridge mediated sliding movement of actomyosin systems, including muscle. This work will utilize simple flagella such as those of sea urchin and tunicate spermatozoa and Chlamydomonas, which can be photographed with high spatial and temporal resolution to obtain detailed descriptions of the movement under a variety of conditions. Computer-assisted methods for analysis of these photographs will be extended by developing fully-computerized methods for analysis of video-digitized images. Most of the experimental work with sperm flagella will utilize ATP-reactivated movement of Triton-demembranated flagella. Major questions that will be addressed will be identification of the trigger for initiation of active sliding in newlyformed bends at the basal end of a flagellum, and characterization of the mechanisms that maintain the angle of propagating bends on flagella. Abnormal bending patterns, generated by a variety of experimental probes, or by mutation (in Chlamydomonas) will be examined in order to functionally dissect the control mechanisms. Interpretation of results will be assisted by using programs for computer simulation of flagellar motility. Efforts will also be made to correlate functional phenomena with specific, known, modifications of flagellar structure or biochemistry, leading us towards a molecular-level understanding of motility control mechanisms. Such modifications include phosphorylation and dephosphorylation, removal of components such as calmodulin or outer arm dynein, a variety of mutations available in Chlamydomonas.